Magnetic tape cartridge having a lower reel recess which is labyrinth-engaged with a stopper ring barrier

ABSTRACT

A magnetic tape cartridge has a reel which includes an upper reel and a lower reel which are plastic moldings, the lower reel being welded to the upper reel by ultrasonic welding. In the shoulder of a boss section of the upper reel, a plurality of recesses are formed in such a manner that the recesses are radially outwardly extended from the center of rotation of the upper reel, and on the surface of the lower reel which are confronted with the recesses, a plurality of welding ribs are formed so as to be engaged with the bottoms of the recesses.

This is a division of application Ser. No. 09/134,040 filed Aug. 14,1998; the entire disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

This invention relates to a magnetic tape cartridge formed by ultrasonicwelding.

In FIG. 1, reference numeral 1 designates the magnetic tape cartridge.The magnetic tape cartridge 1 is constructed as follows: A magnetic tape20 is wound on a reel 3 which is formed by combining upper and lowerreels 4 and 5 together by ultrasonic welding. The reel 3 is rotatablyaccommodated in a cartridge casing which is formed by combining upperand lower cartridges 2 a and 2 b together with screws 19.

The upper reel 4 is made of polycarbonate resin containing glass fibers.The upper reel 4 has an upper flange 4 a, and a recess at the centerwhich has a boss section 4 b extended towards the center. The upperflange 4 a has a gear 4 y on its outer cylindrical surface.

The aforementioned recess has a cylindrical rib, in which a ring-shapedbearing 6 is press-fitted. And a spring plug 7 is fixedly press-fittedin the central hole formed in the bearing. A reel spring 8 is mounted onthe spring plug 7, to push downwardly the aforementioned reel 3 and holdthe reel 3 rotatably.

The lower reel 5 is made of polycarbonate resin, and has a lower flange5 a which has a hole at the center around which an ultrasonic weldingrib 5 b is formed. The lower reel 5 is combined with the shoulder of theaforementioned boss section 4 b.

When the cartridge is not in use, the reel 3 is locked by reel brakes 50and 51 so that it may not be turned unintentionally, the reel brakes 50,51 which are suitably urged by braking torsion springs 12. When themagnetic tape cartridge 1 is not in use, the magnetic tape 20 has beencompletely wound on the reel 3, and the leader tape. 21 connected to theend of the magnetic tape is locked to the end of a hook 18 which isprovided near the side wall of the cartridge.

The opening, through which the magnetic tape 20 is pulled out isdesigned as follows: That is, a lid 30, which is swingable in acartridge plane, is provided while being suitably urged by a torsionspring 15. When the cartridge is not in use, the lid 30 is locked by alocking member 40 (which is suitably urged by a compression spring 16)so that it may not be swung. On the side which is opposite to the sidewhere the lid 13 is provided, the cartridge has a write protect 17.

The aforementioned leader tape 21 is engaged with an engaging meansadapted to lead the magnetic tape 20 in the tape path of the recordingand reproducing device. The leader tape 21 is fastened to the magnetictape 20, for instance, by splicing.

In the above-described magnetic tape cartridge 1, the upper and lowerreels 4 and 5 are combined together by ultrasonic welding as follows. Aswas described before, the annular rib 5 b, which is formed along theannular edge of the circular opening formed at the center of the lowerflange 5 a, is engaged with the shoulder of the lower portion of theboss section 4 b. Under this condition, while a predetermined pressureis applied to the upper and lower reels 4, 5, those reels 3 aresubjected to ultrasonic excitation, so that the rib 5 b is molten tocombine the upper and lower reels 4 and 5 together.

In this welding operation, the upper reel 4 is set below the lower reel5. More specifically, the upper reel 4 is fixedly set, and the lowerreel 5 is placed on the upper reel 4 from above. Under this condition,the upper reel 4 is subjected to ultrasonic pressure excitation. As therib 5 b is molten, the surface of the lower reel 5 is brought intocontact with the shoulder of the upper reel 4. From this fact, it isdetermined that the welding operation has been accomplished.

FIG. 2 shows the conventional ultrasonic welding portions of theaforementioned reel 3. The boss section 4 b of the upper reel 4comprises a shoulder 4 c, and a protrusion 4 d which is extended fromthe shoulder 4 c and is smaller in diameter than the shoulder 4 c. Alongthe outer annular edge of the shoulder 4 c, a stopper ring 4 e isintegrally provided which is slightly higher in level. That is, theupper reel 4 is in the form of a shallow-bottomed container as a whole.In addition, between the stopper ring 4 e and the protrusion 4 d,turn-preventing stoppers 4 f are provided in such a manner that they arediametrically opposite to each other, and are flush with each other.

On the other hand, the rib 5 b of the lower reel 5 has cuts 5 d atangular intervals of 90°. When, with the central hole of the lower reel5 engaged with the protrusion 4 d of the upper reel 4, the lower reel 5is turned, the cuts 5 d are engaged with the turn-preventing stoppers 4f. When, under this condition, the reel 3 is subjected to pressureexcitation, the rib 5 b is molten. The molten portion of the rib 5 b,being absorbed in the shallow-bottomed annular groove, is spreaduniformly. As a result, the surface of the lower flange 5 a is broughtinto contact with the upper surface of the stopper ring 4 e. Thus, thewelding operation has been accomplished.

In the above-described conventional magnetic tape cartridge, the lowerflange 5 a and the stopper ring 4 e are almost in line contact with eachother; that is, they are considerably small in contact area. Hence, itis difficult to weld the upper and lower reels 4, 5 together in such amanner that they are high in parallelism. This fact results in aso-called surface play.

In the case where the tape 20 is wound on the reel 3, the tape windingoperation is carried out with the upper flange 4 a and the boss section4 b of the upper reel 4 as a reference. In this case, since the upperflange 4 a and the boss section 4 b are formed as one unit by injectionmolding, the tape 20 can be wound on the reel 3 with high accuracy.However, in the case where the tape winding operation is carried outbased on the lower reel 5 and the boss section 4 b which suffer from thesurface play, it is difficult to achieve the tape winding operation withhigh accuracy.

If, with the reel 3, the welding area is increased in the direction ofthe diameter, the width of the stopper ring 4 e should be increased.However, in this case, the molten portion flows out of theshallow-bottomed groove; that is, the resultant product is unacceptable.In addition, the welding area is not large enough; that is, the upperand lower reels 4, 5 are not satisfactorily welded together.

In the case of the conventional reels 3 shown in FIG. 2, the lower reel5 is prevented from turning as follows: That is, in order to prevent thelower reel 5 from turning, after the lower reel 5 is set on the upperreel 4, the lower reel 5 must be turned at most 90°. Accordingly, it isimpossible to subject the upper and lower reels 4, 5 to ultrasonic workimmediately after the lower reel 5 is set on the upper reel 4.Furthermore, a metal mold for forming the turn-preventing stoppers 4 fand the cuts 5 d is intricate in configuration. Therefore, there is astrong demand for the provision of turn-preventing means which replacesthe turn-preventing stoppers 4 f and the cuts 5 d.

Furthermore, in the conventional magnetic tape cartridge, as shown inFIG. 3(a) the rib 5 a is molten starting from its end by pressureexcitation, and the molten resin spreads gradually in theshallow-bottomed groove according to the pressure.

However, in practice, as indicated by a group of dots in FIG. 3(b),owing to the pressure which is applied simultaneously when the meltingoperation starts a part of the molten resin sometimes flows over thestopper ring 4 e to the outer periphery of the boss section 4 b. Themolten resin thus caused to over-flow is solidified as cooled, thussticking onto the outer periphery. Hence, when the tape 20 is wound onthe reel 3, the winding center is shifted from the true center; that is,the resultant product is unacceptable.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a magnetic tapecartridge in which the above-described difficulties accompanying aconventional magnetic tape cartridge have been eliminated.

Accordingly, a first object of the invention is to provide a magnetictape cartridge having a reel which is high in weldability, and is soshaped that it is increased in the area of a stopper surface duringwelding, whereby the upper and lower reels are sufficiently high inparallelism.

The first object of the invention has been achieved by the provision ofa magnetic tape cartridge having a reel which comprises an upper reeland a lower reel which are plastic moldings, the lower reel being weldedto the upper reel by ultrasonic welding;

in which, according to the invention,

in the shoulder of a boss section of the upper reel, a plurality ofrecesses are formed in such a manner that the recesses are radiallyoutwardly extended from the center of rotation of the upper reel, and

on the surface of the lower reel which are confronted with the recesses,a plurality of welding ribs are formed so as to be engaged with thebottoms of the recesses.

Furthermore, the first object has been achieved by the provision of amagnetic tape cartridge having a reel which comprises an upper reel anda lower reel which are plastic molding, the lower reel being welded tothe upper reel by ultrasonic welding;

in which, according to the invention,

on a shoulder surrounding the recesses of the upper reel, weldingstopper surfaces are provided in such a manner that the welding stoppersurfaces are scattered circumferentially over the whole width of theshoulder.

According to the invention, during ultrasonic welding, the molten ribsform flows of resin only in the recesses, so that the welding operationis achieved with an amount of welding resin corresponding to the numberand area of recesses.

Furthermore, with the whole surface of the shoulder surrounding therecesses of the upper reel as the stopper surface, the welding surfacespreads radially outwardly, so that the surface contact of the upper andlower reels which have been welded together are high in parallelism.

In the invention, the welding ribs may be extended radially outwardlyfrom the peripheral edge of the central hole of the lower reel, or theymay be curved spirally from the peripheral edge of the central hole, orthey may be protruded in such a manner that they are coaxial with theperipheral edge of the central hole.

A second object of the invention is to provide a magnetic tape cartridgein which the above-described difficulties accompanying a conventionalmagnetic tape cartridge have been eliminated, and in which, immediatelyafter the lower reel is set on the upper reel, those reels can besubjected to ultrasonic welding as they are (without turning the lowerreel), and a reel metal mold is simple in construction.

The second object has been achieved by the provision of a magnetic tapecartridge having a reel which comprises an upper reel and a lower reelwhich are thermoplastic resin moldings, the lower reel being welded tothe upper reel by ultrasonic welding with a welding rib protruded fromthe lower reel abutted against the shoulder of a boss section protrudedfrom the upper reel,

in which, according to the invention,

the surface of the shoulder of the upper reel is roughened.

According to the invention, the lower reel is set on the upper reel, andunder this condition, those reels are pressurized. As a result, thewelding rib is pushed against the roughened surface to provide africtional force which prevents the reels from turningcircumferentially. This makes it possible to subject the reels toultrasonic welding. The surface roughing metal molding is not intricatein structure when compared with the conventional one.

A third object of the invention is to provide a magnetic tape cartridgein which the above-described difficulties accompanying a conventionalmagnetic tape cartridge have been eliminated, and which has a reel inwhich, when the reel is manufactured, the molten resin is prevented fromflowing over the outer periphery of the boss section to prevent theformation of an unsatisfactory product thereby to improve the productyield.

The third object of the invention has been achieved by the provision ofa magnetic tape cartridge having a reel which comprises an upper reeland a lower reel which are thermoplastic resin moldings, the lower reelbeing welded to the upper reel by ultrasonic welding with a welding ribprotruded from the lower reel abutted against the shoulder of a bosssection protruded from the upper reel,

in which, according to the invention,

the surface of the shoulder of the upper reel is roughened.

In the invention, even if, during ultrasonic welding, the molten resintends to flow over the outer periphery in response to a pressurizingforce applied thereto, the over-flow of the molten resin is stoppedbecause the gap provided the walls are narrowed.

The nature, utility and principle of the invention will be more clearlyunderstood from the following detailed description and the appendedclaims when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING(S)

In the accompanying drawings:

FIG. 1 is an exploded perspective view of a conventional magnetic tapecartridge;

FIG. 2 is an exploded perspective view, with parts cut away, showing anexample of the ultrasonic welding section in the conventional magnetictape cartridge;

FIGS. 3(a) and 3(b) are diagrams for a description of the ultrasonicwelding operation in the conventional magnetic tape cartridge;

FIG. 4 is an exploded perspective view, with parts cut away, showing anexample of a magnetic tape cartridge, which constitutes a firstembodiment of the invention;

FIG. 5 is a plan view, with parts cut away, showing the assembly of anupper reel and a lower reel in the first embodiment of the invention;

FIGS. 6(a) and 6(b) are sectional diagrams for a description of thewelding operation of the upper and lower reels;

FIG. 7 is an exploded perspective view, with parts cut away, showinganother example of a magnetic tape cartridge, which constitutes a secondembodiment of the invention;

FIG. 8 is a plan view, with parts cut away, showing the assembly ofan-upper reel and a lower reel in the second embodiment of theinvention;

FIG. 9 is a plan view, with parts cut away, showing the assembly ofupper and lower reels in another example of the magnetic tape cartridge,which constitutes a third embodiment of the invention;

FIG. 10 is an exploded perspective view, with parts cut away, showingupper and lower reels in another example of the magnetic tape cartridge,which constitutes a fourth embodiment of the invention;

FIG. 11 is a sectional half-view showing essential components of thefourth embodiment of the invention;

FIG. 12 is an exploded perspective view, with parts cut away, showingupper and lower reels in another example of the magnetic tape cartridge,which constitutes a fifth embodiment of the invention;

FIG. 13 is an exploded perspective view, with parts cut away, showingupper and lower reels in another example of the magnetic tape cartridge,which constitutes a sixth embodiment of the invention; and

FIGS. 14(a)-14(c) are sectional half-views for a description of thewelding operation of the upper and lower reels in the sixth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will be described with referenceto the accompanying drawings.

First Embodiment

An example of a magnetic tape cartridge, which constitutes a firstembodiment of the invention, will be described with reference to FIGS. 4through 6. In the magnetic tape cartridge, the first embodiment, itsreel is fundamentally equal in configuration to the one in theabove-described conventional magnetic tape cartridge; and in FIGS. 4through 6 parts corresponding functionally to those already describedwith reference to FIGS. 1 through 3 (the conventional magnetic tapecartridge) are therefore designated by the same reference numerals orcharacters.

As shown in FIG. 4, the shoulder 4 c of an upper reel 4 has a protrusion4 d, and has nine (9) recesses 100 in such a manner that the recesses100 are extended radially outwardly from the outer cylindrical surfaceof the protrusion 4 d. Each of the recesses 100 is deeper than theconventional one, and an odd number of recesses 100 are arranged atequal intervals to prevent the mold from bending.

On the other hand, a plurality of welding ribs 102, the number of whichis equal to that of the aforementioned recesses 100, are arranged alongthe peripheral edge of the central hole of the lower reel 5 at equalintervals.

Each of the welding ribs 102 is triangular extending downwardly from thelower flange 5 a, and it is equal in volume to each of the recesses 100.

Therefore, in the gaps between the recesses 100, the whole width W ofthe shoulder 4 c can be utilized as a stopper surface. As shown in FIG.6(a), when the lower reel 5 is slightly turned about the upper reel 4with the lower reel 5 engaged with the upper reel 4, the protrusions 102are fixedly fitted in the recesses 100, respectively. Hence, the upperand lower reels can be subjected to ultrasonic welding.

Accordingly, under this condition, an ultrasonic horn is pushed againstthe whole periphery of the opening of the lower reel 5 as indicated bythe arrow; that is, the upper and lower reels are subjected toultrasonic excitation under a predetermined pressurizing force F. As aresult, the welding ribs 102 are molten in the recesses 100, thusfilling the-recesses 100. Finally, as shown in FIG. 6(b), the lowerflange Sa abuts against the whole surface of the shoulder 4 c. Thus, thelower reel 5 is positioned with respect to the upper reel 4.

In this case, with respect to the contact area in the direction ofdiameter, the whole width W of the shoulder can be utilized. Therefore,the upper and lower reels are maintained high in parallelism. Thewelding area is smaller than that of the conventional magnetic tapecartridge; however, the welding depth is larger, and the number ofwelding parts is plural. Hence, the welding strength is equal to that ofthe conventional magnetic tape cartridge. Furthermore, because of theincrease in welding area, the difference between the load during thewelding operation and that after the welding operation is great, whichmakes it possible to readily achieve the detection of the completion ofthe welding operation with a sensor or the like.

Second Embodiment

Another example of the magnetic tape cartridge, a second embodiment ofthe invention, will be described with reference to FIGS. 7 and 8. As isseen from those figures, the number and interval of the recesses 100 ofthe upper reel 4 are equal to those in the above-described firstembodiment. However, it should be noted that the welding ribs 104 of thelower reel 5 are extended spirally from the periphery of the centralopening. This structure positively prevents the lower reel from turningabout upper reel when compared with that of the first embodiment.

Third Embodiment

Another example of the magnetic tape cartridge, a third embodiment ofthe invention, will be described with reference to FIG. 9. In the thirdembodiment, in the shoulder 4 c, the number of recesses 106 is only five(5); however, they are spread circumferentially. On the other hand, inthe lower reel 5, welding ribs 108 are protruded at equal intervals incorrespondence to the recesses 106 in such a manner that they 108 arecoaxial with the periphery of the central hole.

In the third embodiment, the welding area is larger than that in theabove-described embodiments, while the stopper area is smaller.Therefore, the length of the stopper surface as viewed in the directionof diameter is substantially equal to that in the above-describedembodiment. Hence, the upper and lower reels are maintained high inparallelism.

As is apparent from the above description, in the magnetic tapecartridge of the invention, the reel welding characteristic ismaintained high, and during the welding operation the area of thestopper surface is sufficiently spread: Hence, the upper and lower reelsare sufficiently high in parallelism. This feature prevents the loweringof production yield which may be caused by surface play.

Fourth Embodiment

Another example of the magnetic tape cartridge, a fourth embodiment ofthe invention, will be described with reference to FIGS. 10 and 11. Inthe fourth embodiment, the reel configuration is fundamentally equal tothat in the prior art. Therefore, in FIGS. 10 and 11, partscorresponding functionally to those already described with reference toFIGS. 1 through 3 are therefore designated by the same referencenumerals or characters.

Similarly as in the case of the conventional magnetic tape cartridge, anover-flow preventing stopper ring 4 e is formed around the periphery ofthe shoulder 4 c of the upper reel 4. On the inner periphery of thestopper ring 4 e, a barrier 200 (higher than the stopper ring 4 e) isformed in such a manner that it is protruded from the stopper ring 4 e.

Between the stopper ring 4 e and the protrusion 4 d, a groove 202 isformed coaxial with the stopper ring in such a manner that it is deeper.The inner bottom surface of the groove 202, as shown in FIG. 11, is aroughened surface 204.

On the other hand, the welding rib 5 b of the lower reel 5 has weldingsection 206 on the end which is substantially triangular in section andengaged with the aforementioned deep groove 202. And the outer peripheryof the welding rib 5 b has a recess 208 in such a manner that the formeris coaxial with the latter, and the recess 208 is labyrinth-engaged withthe aforementioned barrier 200.

Hence, when the lower reel 5 is set on the upper reel 4, those reels arelabyrinth-engaged with each other, and the end of the welding section206 is abutted against the roughened surface 204, thus providing africtional force which prevent the circumferential movement of thereels. Hence, the reels can be subjected to the welding operationimmediately. The relative surface roughness of the roughened surface 204to provide the frictional force is preferably 5 to 100 μm in Rz(ten-point average roughness), more preferably 8 to 70 μm, and mostpreferably 10 to 50 μm.

In the following process, the upper and lower reels are subjected toultrasonic excitation while being pressurizing with the ultrasonic horn.As a result, the welding section 206 abutted against the deep groove 202is molten beginning with its end, and the deep groove 202 is alsopartially molten. The molten resin flows to spread in the deep groove202, and tends to flow over the deep groove 202. However, the amount ofover-flow is relatively small because the distance between the shoulderof the welding rib 5 b and the edge of the deep groove 202.

As the process advances, the molten resin caused to flow over the deepgroove 202 tends to pass through the gap between the barrier 200 and therecess 208; however, since the gap is further reduced, the molten resinis detained in the gap between the barrier 202 and the welding rib 5 b,and between the welding rib 5 b and the periphery of the protrusion.Under this condition, the pressure torque variation is detected, and theultrasonic work is accomplished. After the work, the molten material issolidified by cooling, so that the upper and lower reels 4 and 5 areprovided as one unit.

Fifth Embodiment

Another example of the magnetic tape cartridge, a fifth embodiment ofthe invention, will be described with reference to FIG. 12.

The fifth embodiment is different from the fourth embodiment only inthat, instead of the roughened surface 204, a roughened portion 210 isformed which comprises a number of ribs which are radially outwardlyextended. Similarly as in the above-described embodiment, when thewelding portion 206 is engaged with the roughened portion 210, the lowerreel is prevented from turning with respect to the upper reel. In thisconnection, it is preferable that the height of each of the ribs formingthe roughened portion 210 is in a range of from 10 μm to 50 μm.

As is apparent from the above description, the magnetic tape cartridgeof the invention is advantageous in the following points: Even if, afterthe lower reel is set on the upper reel, those reels are subjected toultrasonic treatment, the resultant vibration will never turn the reels.This feature shortens the time required for ultrasonic treatment, andthe metal mold for the magnetic tape cartridge of the invention is notintricate in construction when compared with the one for theconventional magnetic tape cartridge.

Sixth Embodiment

Another example of the magnetic tape cartridge, a sixth embodiment ofthe invention, will be described with reference to FIGS. 13 and 14. Inthe sixth embodiment, the reel is fundamental equal in configuration tothe one in the conventional magnetic tape cartridge. In FIGS. 13 and 14,parts corresponding functionally to those already described withreference to the prior art are therefore designated by the samereference numerals or characters.

Similarly as in the case of the conventional magnetic tape cartridge, anover-flow preventing stopper ring 4 e is protruded from the outerperiphery of the shoulder 4 c of the upper ring 4. Inside the stopperring 4 e, a barrier 300 (larger in height than the former) is protrudedin such a manner that it is extended along the stopper ring 4 e. Adeeper groove 302 is formed between the stopper ring 4 e and theprotrusions 4 d in such a manner that the groove 302 is coaxial with thestopper ring 4 e and the protrusion 4 d.

On the other hand, welding portions 304 are extended from the end of thewelding rib 5 b of the lower reel 5. The welding portions 304 are eachsubstantially triangular in section, and are engaged with theaforementioned deep groove 302. The outer periphery of the welding rib 5b has a recess 306 which is labyrinth-engaged with the barrier 300. Therecess 306 is arranged coaxial with the welding rib 5 b.

Hence, as shown in FIG. 14(a), when the lower-reel 5 is set on the upperreel 4, those reels are labyrinth-engaged with each other.

Under this condition, as shown in FIG. 14(b), the upper and lower reelsare subjected to ultrasonic excitation while being pressurized (thepressurizing force F) with the ultrasonic horn. As a result, the weldingsection 304 abutted against the deep groove 302 is molten beginning withits end, and the deep groove 302 is also partially molten. The moltenresin (indicated by a group of dots in FIG. 14(b) flows to spread in thedeep groove 302, and tends to flow over the deep groove 302. However,the amount of overflow is relatively small because of the distancebetween the shoulder of the welding rib 5 b and the edge of the deepgroove 302.

As the process advances, the molten resin caused to flow over the deepgroove 302, as shown in FIG. 14(c), tends to flow through the gapbetween the barrier 300 and the recess 306; however, since the gap isfurther reduced, the molten resin is detained in the gap between thebarrier 302 and the welding rib 5 b, and between the welding rib 5 b andthe periphery of the protrusion 4 d. Under this condition, the pressuretorque variation is detected, and the ultrasonic work is accomplished.After the work, the molten material is solidified by cooling, so thatthe upper and lower reels 4 and 5 are provided as one unit.

In the above-described embodiment, the ultrasonic welding operation iscarried out with the welding portion 304 of the welding rib 5 b abuttedagainst the deep groove 302. This is to double the labyrinth effect.However, the above-described construction can be simplified with thesame effect. That is, merely by adding the barrier 300 and the recess306 to the structure of the prior art, the over-flow preventing effectcan be obtained.

As is apparent from the above description, in the magnetic tapecartridge of the invention, merely by modifying the configuration of thereel the molten resin can be prevented from flowing over the outerperiphery of the boss section; that is, the lowering of production yieldattributing to the over-flowing of the molten resin can be positivelyprevented.

While there has been described in connection with the preferredembodiments of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention, and it is aimed, therefore, to cover inthe appended claims all such changes and modifications as fall withinthe true spirit and scope of the invention.

What is claimed is:
 1. A magnetic tape cartridge having a reel whichcomprises an upper reel and a lower reel which are thermo-plastic resinmoldings, said lower reel being welded to said upper reel by ultrasonicwelding with a welding rib protruded from said lower reel abuttedagainst the shoulder of a boss section protruded from said upper reel,in which on a part of an over-flow preventing stopper ring which isprotruded from the outer periphery of said shoulder of said upper reel,a barrier is formed which is higher than said part, and on the surfaceof said lower reel which is confronted with said stopper ring, a recessis formed which is labyrinth-engaged with said barrier.